Cross-Sheet and Cross-Workbook References

Help me create formulas that reference other sheets or workbooks:

**Reference Type:**
- [ ] Same workbook, different sheet
- [ ] Different workbook (external reference)
- [ ] Multiple sheets with same structure (3D reference)
- [ ] Dynamic sheet reference (sheet name in cell)

**Source Data:**
- Sheet/Workbook name: [exact name]
- Cell or range to reference: [e.g., B2:B100]
- Data description: [what data is there]

**Destination:**
- Where formula goes: [sheet and cell]
- What calculation needed: [lookup, sum, direct reference, etc.]

**Special Scenarios:**
- [ ] Sheet name contains spaces or special characters
- [ ] Workbook path may change
- [ ] Need to reference multiple similar sheets
- [ ] Sheet name stored in a cell (dynamic reference)
- [ ] Closed workbook reference

**Challenges:**
- [Any specific issues you're encountering]

Please provide:
1. Correct formula syntax
2. Handling special characters in names
3. INDIRECT function for dynamic references
4. Best practices for external links
5. Troubleshooting broken references
6. Performance considerations